The present invention relates to a method for improving the lateral tilt stability of a motor vehicle with at least two axles and two tracks.
In his book xe2x80x9cFundamentals of Vehicle Dynamicsxe2x80x9d, Society of Automotive Engineers, Inc., Warrendale 1992, Chapter 9, p. 309-333, T. D. Gillespie describes different models for roll-over accidents. The conditions for existing tilting risks are calculated beginning with a quasi-stationary model for a rigid motor vehicle and a quasi-stationary model for a resilient motor vehicle up to dynamic models and taking into consideration the natural roll frequency.
When the book was published, it was already known that lorries, trucks, buses, minibuses and off-road vehicles in case of cornering with a large roll movement present a tilting risk due to an elevated center of gravity and/or small track widths, but only recently resulted, that also passenger carsxe2x80x94particularly in case of sinusoidal steering movementsxe2x80x94may build up oscillations which increase to such an extent that they tilt. Such a danger of tilting is increased considerably by inappropriately loading the vehicle, i.e., only on one side or on the vehicle roof, because the position of the mass center of gravity of the motor vehicle is displaced upwardly or to one side.
DE-A 197 46 889 discloses a system for increasing the lateral stability in case of cornering which is provided with a device for detecting the inclination. Said device either measures the level difference between the right and the left side of the vehicle or the transversal acceleration of the vehicle in order to detect the roll angle between the vehicle level and the road level. If said device recognizes a tilting risk, braking the front wheel that is located towards the outside of the bend causes a correcting yawing moment.
As already described above, the admissible transversal acceleration as well as the admissible roll angle depend on the position, in particular the level of the center of gravity of the motor vehicle.
It is thus the object of the present invention to provide a method reacting appropriately to the danger of tilting even in consideration of an unfavorable load.
This object is achieved by not considering the center of gravity of the empty motor vehicle at the beginning of the travel, but the most unfavorable center of gravity of the motor vehicle taking into consideration the admissible vehicle load when a stability threshold is calculated. The stability threshold can be a transversal acceleration or a value correlating with this, for example a yawing rate. But the decision to use the transversal acceleration instead of the yawing rate has the advantage that a metering device for the transversal acceleration which is installed in the vehicle automatically takes into consideration lateral road inclinations, e.g. in super-elevated curves.
The mass distribution existing in the vehicle at the beginning of the travel will not change very much during travel: the passengers might change their seats and the tank level of the vehicle falls. But these are only small and/or slow changes in comparison to the vehicle mass. During travel the sensor technology of the vehicle can make further observations concerning the acceleration and deceleration behavior which serve as a basis for a more precise calculation of the real position of vehicle""s center of gravity.